Re: Questions , Questions ,Questions

["Thomas R. Holtz, Jr." <th81@umail.umd.edu>]

At 05:57 PM 11/20/98 -0800, you wrote:
>I've got a few questions that's been bugging me .
>1. How compelling is the evidence for a monophyletic Ceratosauria ?

Depends on whom you ask...  All recent published studies which include
multiple "ceratosaurs" (Gauthier, 1986; Novas, 1992; Perez-Moreno, 1993;
Holtz, 1994; Sereno et al. 1994, 1996; etc.) find that Ceratosaurus and
Abelisaurus are closer to coelophysoids than to tetanurines.

HOWEVER, all of us in the theropod systematics field have observed and noted
some derived features found in neoceratosaurs (Ceratosaurus and abelisaurs)
which are not found in coelophysoids.  This could be potential evidence that
neoceratosaurs are closer to tetanurines than to coelophysoids.  (In this
case, the neoceratosaur/coelophysoid characters would have to be
convergences and/or primitive neotheropod features lost in Tetanurae).

Rauhut was going to present (at October's SVP meeting) his analysis which
shows that the various neoceratosaur groups were closer to Tetanurae than to
Coelophysoidea.  Unfortunately, he and his poster were a no-show, so we
don't yet know the evidence he used for such a conclusion.

>2. Is there any evidence to indicate that Ceratosaurus may indeed be a
>basal Abelisaur?

Well, most studies find that Ceratosaurus is closer to Abelisauridae than to
Coelophysoidea.  However, because of the ways the various abelisaur taxa are
defined, Ceratosaurus is almost always excluded from this group.  So, close,
but no cigar.

>3. Is there any evidence of a ' subnarial gap ' in any other theropods
>groups outside of Coelophysoidea and Spinosauridae ?

In theropods, no.  In archosauriforms in general, lots of places.  Also, the
anatomical arrangement in coelophysoids differs from the condition in
spinosaurids (although the latter could be derived from the former).
Additionally, now that the postcranial anatomy of spinosaurids are a lot
better known than back in the mid-1980s, there doesn't seem to be much in
the rest of the skeleton to link spinosaurids and coelophysoids.

Hope this helps.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661